Image sensor

ABSTRACT

An image sensor includes a light-sensing element, a first transistor, and a second transistor. The light-sensing element has a first end and a second end electrically connected to a select line. The first transistor has a first end electrically connected to a first control line, a control end electrically connected to the first end, and a second end electrically connected to the first end of the light-sensing element. The second transistor has a first end electrically connected to a voltage source, a control end electrically connected to the first end of the light-sensing element, and a second end electrically connected to an output line. The light-sensing element uses the material of silicon rich oxide so that the light-sensing element can sense the luminance variance and have the characteristic of the capacitor for the level boost.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to an image sensor, and moreparticularly, to an image sensor formed by the silicon rich oxidematerial.

2. Description of the Prior Art

The conventional image sensor utilizes the built-in amplifier componentof each pixel to amplify the photoelectric conversion signal. Each pixelthen utilizes the XY addressing method to select for obtaining thevoltage level of the photoelectric conversion signal. Since each pixelincludes the built-in amplifier component, the photoelectric component(i.e. the light sensing component) generates the sensing signal of photocharges when beamed with light, and the sensing signal is amplified bythe built-in amplifier component accordingly. This way, the sensingsignal is not easily affected by the noise when being transmitted fromthe photoelectric component to the external control circuit. From thecircuit design's point of view, the sensitivity of the image sensor isdependent on three main factors. The first factor is the area of thelight sensing component. Fundamentally, the area of the light sensingcomponent is directly proportional to the intensity of the sensed photocharges under identical luminance; increasing the area of the lightsensing component increases the photo charges generated by the lightsensing component. The second factor is the capacitance of theintegrating capacitor. Theoretically, under the same stored electricalcharge, the voltage at the two ends of the capacitor is inverselyproportional to the capacitance; increasing the capacitance decreasesthe voltage at the two ends of the capacitor. The third factor is thegain of the sensing amplifier of the light sensing component.

SUMMARY OF THE INVENTION

The present invention discloses an image sensor. The image sensorcomprises a light sensing component, a first transistor and a secondtransistor. The light sensing component has a first end, and a second.The second end is electrically connected to a select line. The firsttransistor has a first end electrically connected to a first controlline, a control end electrically connected to the first end, and asecond end electrically connected to the first end of the light sensingcomponent. The second transistor has a first end electrically connectedto a voltage source, a control end electrically connected to the firstend of the light sensing component, and a second end electricallyconnected to an output line.

The present invention further discloses an image sensor. The imagesensor comprises a light sensing component, a diode and a sourcefollower. The light sensing component has a first end, and a second endelectrically connected to a select line. The diode has a first endelectrically connected to a control line, and a second end electricallyconnected to the first end of the light sensing component. The sourcefollower has an input end electrically connected to the first end of thelight sensing component, and an output end electrically connected to anoutput line, for outputting a sensing voltage generated by the lightsensing component.

The present invention further discloses a method for detecting theluminance variation by using an image sensor, the image sensorcomprising a light sensing component having a first end and a second endelectrically connected to a select line; a first transistor having afirst end electrically connected to a control line, a control endelectrically connected to the first end and a second end electricallyconnected to the first end of the light sensing component; and a secondtransistor having a first end electrically connected to a voltagesource, a control end electrically connected to the first end of thelight sensing component and a second end electrically connected to anoutput line. The method comprises the control line transmitting a highlevel voltage to turn on the first transistor, for resetting a voltagelevel of the light sensing component; the control line transmitting alow level voltage to turn off the first transistor, for the lightsensing component to generate a voltage drop when sensing light; and theselect line transmitting the high level voltage for transmitting thevoltage drop to the output line via the second transistor.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating the image sensor according tothe first embodiment of the present invention.

FIG. 2 is a waveform diagram illustrating the operation sequence of theimage sensor of the present invention.

FIG. 3 is a diagram illustrating the cross-section view of the imagesensor of the present invention.

FIG. 4 is a diagram illustrating the image sensor according to thesecond embodiment of the present invention.

FIG. 5 is a diagram illustrating the image sensor according to the thirdembodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1. FIG. 1 is a circuit diagram illustrating theimage sensor 30 according to the first embodiment of the presentinvention. The light sensor 30 comprises a first transistor 21, a lightsensing component 22, a second transistor 24 and a reference currentsource 25. In the present invention, the light sensing component 22 canbe realized with a capacitor formed by a metal layer, a silicon richoxide layer and a transparent metal layer, wherein the transparent metallayer can be made of Indium Tin Oxide (ITO). One end of the lightsensing component 22 is electrically connected to the row select line S2and the other end of the light sensing component 22 is electricallyconnected to the source electrode of the first transistor 21 and thegate electrode of the second transistor 24. The gate electrode and thesource electrode of the first transistor 21 are electrically connectedto form a diode component which is controlled by the reset signal lineS1. The drain electrode of the second transistor 24 is electricallyconnected to the voltage source VDD; the gate electrode of the secondtransistor 24 is electrically connected to the light sensing component22 and the source electrode of the transistor 21, forming a sourcefollower which functions as the capacitance-voltage amplifier; thesource electrode of the second transistor 24 is electrically connectedto the column output line S3. The reference current source 25 iselectrically connected to the column output line S3, the referencecurrent source 25 provides the output current according to a referencevoltage VREF.

Please refer to FIG. 2. FIG. 2 is a waveform diagram illustrating theoperation sequence of the image sensor 30 of the present invention. Theoperation sequence of the image sensor 30 can be roughly categorizedinto the reset phase TO, the integration phase T1 and the reading phaseT2. The operation sequence of the image sensor 30 is explained as below:

Step 1: When the reset signal S1 is at the low voltage level (VSS), thevoltage level of the node A3 of the light sensing component 22 isfloating. When the reset signal S1 is converted from the low voltagelevel (VSS) to the high voltage level (VREF), the image sensor 30 entersthe reset phase T0, and the diode component formed by the firsttransistor 21 is turned on due to the component operating in forwardbias. When the reset signal line S1 is at the high voltage level (VREF),the node A3 of the light sensing component 22 is charged to the voltagelevel of (VREF−Vth) since the diode component is operating in forwardbias, wherein Vth represents the threshold voltage of the firsttransistor 21.

Step 2: When the reset signal S1 is converted from the high voltagelevel (VREF) to the low voltage level (VSS), the diode component formedby the first transistor 21 is turned off due to the component operatingin reverse bias. At the moment the voltage drop between the two ends ofthe light sensing component 22 is (VREF−Vth)−VSS, and the voltage levelof the node A3 of the light sensing component 22 is floating; the imagesensor 30 enters the integration phase T1.

Step 3: when the image sensor 30 is in the integration phase T1, thevoltage level of the node A3 of the light sensing component 22 variesaccording to the luminance of the incident light. When the light sensingcomponent 22 is beamed with light, the node A3 of the light sensingcomponent 22 generates photo charges. The generated photo chargesneutralize the stored charges of the node A3 of the light sensingcomponent 22, diminishing the voltage drop between the two ends of thelight sensing component 22. The higher the luminance of the incidentlight, the lower the voltage level of the node A3 of the light sensingcomponent 22. For instances, when the light luminance B is greater thanthe light luminance A (i.e. Lux B>Lux A), the gradient of the decreasingrate of the voltage level of the node A3 for the light luminance A isalso greater than that of the light luminance B (i.e. mB>mA)

Step 4: Since the diode component of the first transistor 21 is turnedoff due to the component operating in reverse bias, the voltage level ofthe node A3 of the light sensing component 22 is still floating. Whenthe row select line S2 is converted from the low voltage level (VSS) tothe high voltage level (VREF), the voltage level of the node A3increases by (VREF−VSS) accordingly, as the voltage drop between the twoends of the light sensing component 22 (with characteristics of acapacitor) does not change instantaneously.

Step 5: When the voltage level of the node A3 of the light sensingcomponent 22 has increased by (VREF−VSS) due to the light sensingcomponent 22 with the characteristics of the capacitor, the voltagelevel of the node A3 is sufficient to turn on the second transistor 24of the source follower.

Step 6: When the second transistor 24 of the source follower is turnedon, the signal (equivalent to the voltage level of the node A4) of thecolumn output line S3 is equivalent to the increased voltage level ofthe node A3 of the light sensing component 22 subtracting the thresholdvoltage Vth of the second transistor 24. For instances, the signal ofthe column output line S3 is (VA−Vth) for the light luminance Lux A and(VB−Vth) for the light luminance Lux B.

Please refer to FIG. 3. FIG. 3 is a diagram illustrating thecross-section view of the image sensor 30 of the present invention. Afirst transistor 21 and a second transistor 24 are formed on thesubstrate 31. A gate oxide layer 32, a first insulation layer 33 and asecond insulation layer 34 are formed between the first transistor 21,the second transistor 24 and the light sensing component 22. The firsttransistor 21 is an N-type Metal Oxide Semiconductor (NMOS) transistor,comprises a gate electrode 211, a source electrode 212 and a drainelectrode 213. The second transistor 24 is an NMOS transistor, comprisesa gate electrode 241, a source electrode 242 and a drain electrode 243.The light sensing component 22 comprises a metal layer 221, a siliconrich oxide layer 222 and a transparent metal layer 223.

Please refer to FIG. 4. FIG. 4 is a diagram illustrating the imagesensor 50 according to the second embodiment of the present invention.The image sensor comprises a first transistor 51, a light sensingcomponent 52, a second transistor 54 and a third transistor 55. In thesecond embodiment, the third transistor 55 is utilized to replace thereference current source 25. The row output line S3 is electricallyconnected to the drain electrode of the third transistor 55; the gateelectrode of the third transistor 55 is controlled by the signal lineVb; the source electrode of the third transistor 55 is electricallyconnected to the reference voltage source VREF.

Please refer to FIG. 5. FIG. 5 is a diagram illustrating the imagesensor 60 according to the third embodiment of the present invention.The image sensor 60 comprises a diode 61, a light sensing component 62,a second transistor 64, a sampling capacitor 65 and a third transistor66. In the third embodiment, the sampling capacitor 65 and the thirdtransistor 66 are utilized to replace the reference current source 25.In addition, the diode 61 also replaces the first transistor 21. The rowoutput line S3 is electrically connected to the drain electrode of thethird transistor 65 and one end of the sampling capacitor 65; the gateelectrode of the third transistor 65 is controlled by the signal lineREST2; the source electrode of the third transistor 65 is electricallyconnected to the other end of the sampling capacitor 65 and thereference voltage source VREF.

In conclusion, the image sensor of the present invention comprises alight sensing component, a first transistor and a second transistor. Thelight sensing component comprises a first end and a second endelectrically connected to a select line. The first transistor comprisesa first end electrically connected to a first control line, a controlend electrically connected to the first end, and a second endelectrically connected to the first end of the light sensing component.The second transistor comprises a first end electrically connected to avoltage source, a control end electrically connected to the first end ofthe light sensing component, and a second end electrically connected toan output line. The light sensing component is made of silicon richoxide material, so the light sensing component is able to detect thevariation of the light luminance. At the same time, the light sensingcomponent possesses the characteristics of the integrating capacitor,and can be utilized for increasing the corresponding voltage level.Therefore, the image sensor of the present invention utilizes twotransistors and the light sensing component made of the silicon richoxide material, for simplifying the circuit structure.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention.

What is claimed is:
 1. An image sensor, comprising: a light sensingcomponent, having a first end and a second end, the second endelectrically connected to a select line; a first transistor having afirst end electrically connected to a first control line, a control endelectrically connected to the first end, and a second end electricallyconnected to the first end of the light sensing component; and a secondtransistor having a first end electrically connected to a voltagesource, a control end electrically connected to the first end of thelight sensing component, and a second end electrically connected to anoutput line.
 2. The image sensor of claim 1, further comprising: acurrent source, electrically connected to the output line.
 3. The imagesensor of claim 2, wherein the current source comprises: a thirdtransistor having a first end electrically connected to the output line,a control end electrically connected to a second control line, and asecond end electrically connected to a reference voltage source.
 4. Theimage sensor of claim 3, wherein the current source further comprises: acapacitor, having a first end electrically connected to the output line,and a second end electrically connected to the reference voltage source.5. The image sensor of claim 1, wherein the light sensing componentcomprises: a metal layer electrically connected to the second end of thefirst transistor; a transparent metal layer electrically connected tothe select line; and a silicon rich oxide layer disposed between themetal layer and the transparent metal layer.
 6. An image sensor,comprising: a light sensing component, having a first end, and a secondend electrically connected to a select line; a diode, having a first endelectrically connected to a control line, and a second end electricallyconnected to the first end of the light sensing component; and a sourcefollower, having an input end electrically connected to the first end ofthe light sensing component, and an output end electrically connected toan output line, for outputting a sensing voltage generated by the lightsensing component.
 7. The image sensor of claim 6, further comprising: acurrent source, electrically connected to the output line.
 8. The imagesensor of claim 6, further comprising: a voltage source, electricallyconnected to the source follower.
 9. The image sensor of claim 8,wherein the source follower comprises: a transistor, having a drainelectrode electrically connected to the voltage source, a gate electrodeelectrically connected to the first end of the light sensing component,and a source electrode electrically connected to the output line. 10.The image sensor of claim 6, wherein the light sensing componentcomprises: a metal layer, electrically connected to the source follower;a transparent metal layer, electrically connected to the select line;and a silicon rich oxide layer, formed between the metal layer and thetransparent metal layer.
 11. A method for detecting the luminancevariation by using an image sensor, the image sensor comprising a lightsensing component having a first end and a second end electricallyconnected to a select line; a first transistor having a first endelectrically connected to a control line, a control end electricallyconnected to the first end and a second end electrically connected tothe first end of the light sensing component; and a second transistorhaving a first end electrically connected to a voltage source, a controlend electrically connected to the first end of the light sensingcomponent and a second end electrically connected to an output line, themethod comprising: transmitting a high level voltage by the control lineto turn on the first transistor, for resetting a voltage level of thelight sensing component; transmitting a low level voltage by the controlline to turn off the first transistor so as to have the light sensingcomponent generate a voltage drop; and transmitting the high levelvoltage by the select line for transmitting the voltage drop to theoutput line via the second transistor.